In recent years, from the viewpoint of environmental protection and effective use of resources, there has been a demand for technology for efficiently sorting and reprocessing waste products. The reuse of rare metal resources leads to a reduction in processing cost as well. For this reason, there has been a demand for technology for efficiently reprocessing shadow masks of CRT displays (hereinafter, called a “CRT shadow mask”) that are widely used as displays devices in TVs and personal computers. A shadow mask is a metal plate in which small holes are regularly aligned in a honeycomb configuration. In CRT displays, a shadow mask is disposed between an electron gun and phosphor so that when the phosphor is irradiated with a beam from the electron gun, excess portions of the beam are blocked in order to make the pixel pitch smaller. In the process for recycling CRT displays, the shadow mask and support members for the shadow mask are removed from the CRT and recycled as metal resources.
Shadow masks are formed mainly from iron or an Invar alloy that is 64% iron and 36% nickel, which is normally called Invar 36. In recent years, along with increasing screen sizes and the flattening of CRT displays, Invar 36 (hereinafter, called “Invar” or “Invar alloy”) has become applied widely to shadow masks due to having little thermal expansion, which is called the Invar property. Since Invar alloy includes nickel, which is valuable, the recovery of shadow masks that are made of Invar alloy is very beneficial in metal resource recycling and the reduction of recycling cost. Therefore, the identification of the metal composition of shadow masks is an important issue in metal recycling. Conventionally, the metal composition of shadow masks has been identified by, for example, human judgment using visual observation, tactile sensation or the like, which requires experience, or by analyzing devices that use X-ray fluorescence or the like, which requires advanced technology and large and expensive equipment.
Examples of the methods for identifying the material of a metal plate such as a vehicular plate include a method of identification by measuring electrical resistance (e.g., Patent Documents 1 and 2), and a method of identification by generating an arc discharge between a discharge electrode and a metal sample and performing spectral analysis on light emitted along with the discharge (e.g., Patent Document 3). Additionally, there is a method of identification by an optical method using a surface coating property of a metal plate product in a conveyor line for metal plate products in a manufacturing process (e.g., Patent Document 4), a method of identification by X-ray fluorescence analysis of a metal such as iron that is contained as an impurity in a thin film on a semiconductor substrate (e.g., Patent Document 5), a method of automatic identification by performing image processing on, among foreign matter contained in a solution, foreign matter that has metallic luster and foreign matter that does not have metallic luster (e.g., Patent Document 6), and a method of identifying a work material based on an absorption spectrum (e.g., Patent Document 7).    Patent document 1: JP 2002-28789A    Patent document 2: JP S61-10755A    Patent document 3: JP H07-318495A    Patent document 4: JP 2005-534915A    Patent document 5: JP 2006-53012A    Patent document 6: JP H08-178843A    Patent document 7: JP 2000-180261A